# Z axis crashing into touch probe - why? **URL:** \ **Category:** General Chat\ **Created:** [September 13, 2026, 1:45pm UTC](https://forum.avidcnc.com/t/z-axis-crashing-into-touch-probe-why/6581 "2026-09-13T13:45:40Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![AlwaysLearning](https://avatars.discourse-cdn.com/v4/letter/a/858c86/32.png) [@AlwaysLearning](https://forum.avidcnc.com/u/AlwaysLearning)\ **Post date:** [September 13, 2026, 1:45pm UTC](https://forum.avidcnc.com/t/z-axis-crashing-into-touch-probe-why/6581/1 "2026-09-13T13:45:40Z")
After homing the machine, I jog X, Y, and Z to near the corner of my 19mm thick MDF part. I then position the TP on the corner of the part and connect the magnet to the 12.7mm end mill. At this point, I like to pick up the TP and touch it to the bit to confirm the indicator shows Active - it does. I then select the upper left corner icon in the probe routine. Normally, the Z moves slowly closer to the TP until it makes contact then backs off. But now it moves much too fast and crashes into the TP and I am at a loss to understand why. I cycled power on everything and tried again with the same results - I hit the EStop button before it hit the TP. The machine ran fine just before this, but I did make one change: I switched the machine to metric units from inches. I suspect this is somehow at the root of the problem, but all the machine settings appear to be correct. Here’s a screen shot of the current settings (I have never changed these) ![image](https://canada1.discourse-cdn.com/flex027/uploads/avidcnc/original/2X/b/bfcc71dd05ff67fb4813112c63059a8539d25f25.jpeg) I’m thinking my next step should be to reload the machine profile(?) ---
**Author:** ![AlwaysLearning](https://avatars.discourse-cdn.com/v4/letter/a/858c86/32.png) [@AlwaysLearning](https://forum.avidcnc.com/u/AlwaysLearning)\ **Post date:** [September 13, 2026, 11:12pm UTC](https://forum.avidcnc.com/t/z-axis-crashing-into-touch-probe-why/6581/2 "2026-09-13T23:12:21Z")
Although it’s not at all clear to me why this resolved the issue, reloading the machine profile did the trick. I used the Mach 4 GUI tool to restore from an earlier backup file, in case anyone is curious. ---
**Author:** ![TimG](https://avatars.discourse-cdn.com/v4/letter/t/82dd89/32.png) [@TimG](https://forum.avidcnc.com/u/TimG)\ **Post date:** [September 14, 2026, 1:04am UTC](https://forum.avidcnc.com/t/z-axis-crashing-into-touch-probe-why/6581/3 "2026-09-14T01:04:41Z")
I’m curious if the old profile you reloaded was in inches or metric and if in inches did you change it to metric, then it worked this time. Thanks! ---
**Author:** ![da-kengineer-meister](https://avatars.discourse-cdn.com/v4/letter/d/f1d935/32.png) [@da-kengineer-meister](https://forum.avidcnc.com/u/da-kengineer-meister)\ **Post date:** [September 14, 2026, 4:56am UTC](https://forum.avidcnc.com/t/z-axis-crashing-into-touch-probe-why/6581/4 "2026-09-14T04:56:46Z")
I had this problem in the previous version of the software. Took a bit of work to figure out, but the root cause was that the routine I was running just before using the touch probe left in it relative mode. (G91 mode) In my case going into the MDI screen and executing a G90 to bring the software back to absolute mode was enough the cure the problem. Not sure if this is the exact problem you are having but it may add a little more data to the problem solving you are doing. ---
**Author:** ![AlwaysLearning](https://avatars.discourse-cdn.com/v4/letter/a/858c86/32.png) [@AlwaysLearning](https://forum.avidcnc.com/u/AlwaysLearning)\ **Post date:** [September 14, 2026, 2:18pm UTC](https://forum.avidcnc.com/t/z-axis-crashing-into-touch-probe-why/6581/5 "2026-09-14T14:18:23Z")
Both the current and old (reloaded) profiles were G20 (metric). hth